Prior art underwater lighting fixtures have used gas discharge or incandescent filaments housed in thin glass envelopes as the light source. These glass envelopes collapse at depths as shallow as 100-ft, and cannot operate in contact with any liquids. To go any deeper, these glass envelopes must be protected from direct ocean pressure to prevent them from imploding. Typical designs use a glass dome or flat window, with a metal or heavy plastic housing. A pressure proof underwater electrical bulkhead connector brings electrical power across the interface.
FIG. 1 illustrates a Multi SeaLite® light fixture 102 commercially available from DeepSea Power & Light of San Diego, Calif., assignee of the instant application. The light fixture 102 utilizes a halogen gas-filled glass envelope lamp that must be protected from direct exposure to high ocean pressure. More particularly, referring to FIG. 2, a halogen lamp 204 is included in the light fixture 102. The halogen lamp 204 includes a thin inert gas-filled glass envelope that is only designed to survive atmospheric pressure differences found in typical applications from sea level to mountain tops. In order to survive at great ocean depths, e.g. 3,000 meters, the light fixture 102 includes a pressure protected housing is comprised of a glass hemisphere 202, metal back shell 206, cowl 212, and bulkhead connector 210. An internal reflector 214 redirects lights from the halogen lamp 204 forward through the glass hemisphere 202. A mount 208 permits the light assembly to attach to a manned or remotely piloted submarine. See U.S. Pat. Nos. 4,683,523 and 4,996,635 both of Mark S. Olsson et al. for further details regarding the construction of light fixture 102.
Recently, high brightness light emitting diodes (LEDs) have begun to be used in terrestrial markets as a reliable, efficient solid state light source capable of narrow or wide chromatic bandwidth. FIG. 3A illustrates an individual Cree XRE high brightness LED 302. It comprises light-emitting die 306 (FIG. 3B) illustrated centrally situated above a ceramic base 312, encapsulated with silicone gel 310, contained by a metallic ring 308, that supports a transparent dome-shaped lens element 304. Electrical contacts 314 and 320 are placed on top of the ceramic base 312, and a duplicate pair 316 and 322 are placed on the underside. A thermal-transfer pad 318 is also located in the center of the underside of the ceramic base to aid in drawing heat away from the die 306.
It would be desirable to provide a deep submersible light that takes advantage of the new high brightness LEDs that have become commercially available. LEDs in such a light can accommodate very high ambient water pressures directly, but due to the electrical nature of the LEDs requires that they be isolated from seawater, which is electrically conductive.